Meeting Abstract
Pinnipeds are a group of marine mammals with three extant families: Otariidae, which includes fur seals and sea lions; Phocidae, the true seals; and Odobenidae, the walrus. They are unique among marine mammals because of their amphibious lifestyle and the retention of two forms of insulation, fur and blubber. Fur and blubber thicknesses are variable among the pinniped groups: fur seals have dense, waterproof fur and a moderate blubber layer; sea lions have non-waterproof fur with a thicker blubber layer; phocids have thin, non-waterproof fur with very thick blubber; and walruses have almost no fur and the thickest blubber. Fur seal and sea lion pelts have a similar thermal conductivity in air, whereas phocid seal pelts have a higher conductivity and therefore reduced function in air. However, the thermal function of the pelt in water has never been quantitatively compared between groups. This study examined the effects of submergence on the thermal function of pinniped pelts by measuring the thermal conductivity and thermal resistance of otariid and phocid pelts in water. Under conditions of submergence, fur seal pelts (N=17) had the lowest thermal conductivity; sea lion (N=21) and phocid (N=9) pelts had significantly higher thermal conductivities (P<0.001). Taking fur thickness into account, fur seal pelts had the highest thermal resistance in water (P<0.001), whereas sea lion and phocid seal pelts had lower and nearly equal thermal resistance values. Although fur seal and sea lion pelts function similarly in air, the ability of the fur seal pelt to trap air while submerged makes it a superior insulator in water. In contrast, sea lions and phocids must depend on their blubber for insulation when submerged. Overall, this has implications for the evolutionary transition from fur to blubber in these groups, especially within the Otariidae.
